1. Field of the Invention
The present invention relates to a numerical controller with abnormal motor deceleration stop control means, and more particularly, to a technique for urgently stopping a motor of a machine controlled by a numerical controller in case of occurrence of an abnormality at a numerical control section of the numerical controller.
2. Description of the Related Art
A numerical controller is composed of a servo section, a programmable machine controller section (hereinafter referred to as PMC section), and a numerical control section. The servo section controls a motor attached to a machine that is controlled by the numerical controller. The PMC section controls DI/DO signals (input/output signals) for the machine. The numerical control section outputs commands to and exchanges data with the servo section and the PMC section.
FIG. 2 is a schematic diagram showing a system including a conventional numerical controller 10′ and a machine 24 that is controlled by the controller 10′. A servo section 15 controls the position, speed, and current of a motor 22 for each axis of the machine 24 in response to a move command from a numerical control section 11. Further, a PMC section 16 enables an I/O control section (hereinafter referred to as I/O unit) 23 to control DI/DO signals for the machine 24. In the case where a movable axis of the machine moves under the influence of an external force, such as the gravity, in particular, the motor that drives the movable axis is provided with a brake device. This brake device can be on/off-controlled by the I/O unit 23 based on a DO signal from the PMC section 16. Further provided is an abnormality detection circuit 14 that detects an abnormality of the numerical control section 11.
The numerical control section 11 executes a control program, thereby distributing a move command to the servo section 15 that drivingly controls the motor for each axis of the machine 24. Based on this move command and position and speed feedback signals fed back from position and speed detectors (not shown), the servo section 15 performs position and speed feedback control and current feedback control and outputs a drive command to an amplifier 21. The amplifier 21 performs PWM control or the like and drivingly controls the motor 22. On the other hand, the PMC section 16 transmits and receives DI/DO signals through the I/O unit 23, and causes the I/O unit 23 to on/off-control sensors and actuators attached to the machine 24, peripheral equipment, etc. As mentioned before, the brake device that is attached to the motor 22 is also on/off-controlled by the DO signal (output signal).
In the numerical controller 10′, as described above, the servo section 15 drivingly controls the motor that drives the movable axis of the machine, and the PMC section 16 receives signals from the various sensors, on/off-controls the various actuators and the peripheral equipment, and drivingly controls the machine 24.
If the abnormality detection circuit 14 detects an abnormality of the numerical control section 11 while the numerical controller 10′ is operating, it outputs an abnormality detection signal to the servo section 15. On receipt of this abnormality detection signal, the servo section 15 stops a drive command signal for the amplifier 21. When the drive command signal is stopped, the amplifier 21 interrupts power supply to the motor 22. When the power supply to the motor 22 is interrupted, dynamic braking is applied by the motor 22, whereupon a movement of a moving part is stopped.
On the other hand, the PMC section 16 periodically exchanges data with the numerical control section 11. If the exchange of the data with the numerical control section 11 is interrupted for a fixed period of time or longer, it is concluded that an abnormality has occurred, and all the DO signals (output signals) are turned off. When the DO signals are turned off, the brake device that is attached to the motor 22 is worked to brake the motor 22.
The conventional numerical control system performs emergency stop control such as the aforementioned one if an abnormality occurs in the numerical control section 11.
In order to ensure an operator's safety when the numerical control system is urgently stopped, moreover, a sensor is provided for detecting a dangerous state, if any, of the operator. In response to a signal from the sensor, the motor is cut off from the power supply and stopped. According to a known invention (see Japanese Patent Application Laid-Open No. 5-146940), in this case, the interruption of the power supply is detected by alarm detection means and an alarm output is delivered. If the power supply to the motor is interrupted in response to the signal from the sensor, the alarm detection means is inactivated by the sensor signal lest an alarm be output, whereby the recovery of the system is facilitated.
In the prior art technique described above, the rotation of the motor and the movement of the moving part that is driven by the motor are stopped by interrupting the power supply to the motor in case of an emergency stop. In stopping the motor rotation and the movement of the moving part when an abnormality occurs during a high-speed movement, therefore, the motor power supply is only interrupted, so that the motor and the moving part coast for long distances.
If the moving part is a gravity axis or the like that is vertically moved by an external force other than a force from the motor, moreover, it inevitably moves under the influence of the gravity or any other external force even when the power supply to the motor is interrupted. Accordingly, the brake device is attached to the motor that drives the moving part so that the movement of the moving part can be stopped by braking the motor by means of the brake device when the power supply to the motor is interrupted, as mentioned before.
In the conventional method described above, however, the operation for stopping the motor and the timing for a brake signal are not controlled. If the output of the brake signal is delayed behind the motor stop, therefore, the moving part, including the gravity axis, unfavorably drops and moves before it is braked.